Sounds Fishy To Me

A worrying increase in the number of reports of oxygen minimum zones (OMZs) in the world's oceans has important implications for fisheries and for climate change. OMZs are intense sites of denitrification, which contributes significantly to levels of atmospheric N2O, an important greenhouse gas that also depletes ozone. The ecological sequelae of OMZ formation can be profound because few species are able to avoid or tolerate extreme oxygen depletion. Consequently, where the upper depth limit of the OMZ approaches the surface, there is less vertical habitat available for pelagic organisms. Acoustic echoes reflect off small fish and zooplankton; where the echoes stop, life stops, and here lies the oxycline. Bertrand et al. have used this method off the coast of Peru, where the world's largest anchovy fishery is fed by a huge upwelling of nutrients associated with an OMZ. They estimated from survey data that the volume of oxygenated water available to the fishery was about 9000 km3 and ranged from a depth of 15 to 140 m with a marked latitudinal gradient. This method not only can be used to monitor changes in the oxycline but also offers a picture of the structure of an otherwise apparently featureless environment.

PLoS ONE5, e10330 (2010).

Microbiology

The Worth of Coppers

Gilbert Chin

The immense reach of microbial sequencing projects has outstripped the capacity of physiology (with its reliance on cultivatable organisms) and biochemistry (ditto for purified enzymes) to exploit these data sets—apart from exceptional efforts, of which the discovery of a fourth pathway for oxygen evolution by Ettwig et al. is the most recent. Using comparative bioinformatics and a bit of old-fashioned guesswork, Walker et al. provide a plausible picture of the lifestyle of the marine archeon Nitrosopumilus maritimus. It falls into a class of microbes that oxidize ammonia to hydroxylamine and thence to nitrite. Doing so yields hydrogen ions and electrons. Unlike ammonia-oxidizing bacteria that depend on heme(iron)-based proteins for the chemical and electron transfer reactions, Nitrosopumilus hews to a copper-based economy, encoding several varieties of multicopper oxidases and plastocyanin-like carriers. This apparent relief from a heavy dependence on iron, coupled to the high affinity of its ammonia monooxygenase and energy-efficient mode of carbon fixation, may account for its ecological success.

An Up Side to Humidity

Jake Yeston

Concerns over the climatic impact of rising CO2 levels in the atmosphere have led to a flurry of research activity directed toward capturing the gas as it's released from power plants and ultimately burying it in the ground. An efficient process along these lines would require a sorbent that attracted CO2 vigorously and quickly, yet formed a weak enough bond to facilitate release into a concentrated stream bound for the sequestration well. Sayari and Belmabkhout show in this context that humidifying a CO2 stream helps to maintain the robustness of amine-bearing solid sorbents. Through solid-state nuclear magnetic resonance spectroscopy, the authors found that dry CO2 can react with two amine sites, forming a urea [N−(C=O)−N] linkage with concomitant loss of water that traps the carbon too tightly and inhibits regeneration of the free sorbent. Adding water restricts the binding motif to a single N-C bond, which is more easily broken on heating, allowing more than 700 sorption/desorption cycles without substantial efficiency loss. Moreover, deactivated sorbents could be regenerated by day-long heating under humid N.

J. Am. Chem. Soc.132, 10.1021/ja1013773 (2010).

Climate Science

Unlucky Seven

Based on what we know about how atmospheric CO2 affects Earth's energy balance, how heat is distributed in the climate system, and how the concentration of CO2 in the atmosphere is likely to change over the next century, the global average surface air temperature in the year 2100 is projected to be 3° to 4°C higher than it is today. That is just a best estimate, however, and the temperature increase could be lower, if we are lucky, or higher—even much higher—if we are not so lucky. How could a larger than expected increase in temperature affect humans? Sherwood and Huber consider how much heat stress human metabolism can withstand. They contend that prolonged exposure to temperatures of 35°C would be intolerable, even fatal, and determine with a climate model that a global mean surface temperature increase of only 7°C would create certain zones in which temperatures would routinely rise above the tolerable threshold; with more time, or the misfortune of the climate's proving more sensitive to rising CO2 than we realize, temperature increases of 10°C or more could make much of the populated area of the planet uninhabitable. Though such large temperature increases may not be likely, still they are possible, and the potential consequences should not be ignored.

Proc. Natl. Acad. Sci. U.S.A.107, 10.1073/pnas.0913352107 (2010).

Physics

Lone Proton

Ian S. Osborne

A small test mass attached to a spring and driven to oscillate will furnish information on the mechanical properties of the spring itself and also the medium in which it is immersed. In a similar fashion, probing the oscillation frequency of a single trapped electron provides knowledge of the magnetic moment of the electron (the test mass) as well as a precise knowledge of its electromagnetic environment by way of the fine structure constant. As matter is made up of electrons, protons, and neutrons, it seems natural to ask how the magnetic properties of all the elementary particles arise. However, because the magnetic properties of nucleons are much weaker than those of electrons, correspondingly precise measurements become very challenging. Hoping to change that situation, Guise et al. have developed a technique to trap and probe a single proton (or antiproton). The asymmetries between matter and antimatter can also be addressed in this context at the fundamental level.

Phys. Rev. Lett.104, 143001 (2010).

Development

Jack of All Trades

L. Bryan Ray

The efficiency with which organisms operate compels many proteins to function in more than one way and often at more than one location. TAZ is a protein that acts with other proteins to regulate transcription in response to activation of the Hippo signal transduction pathway, which controls cell proliferation and organ size, and TAZ can move between the nucleus and the cytoplasm; but that's not all. Varelas et al. looked for genes that influence signaling by the Wnt proteins, which are secreted morphogens that control proliferation and cell fate in developing tissues, and found TAZ. Mice lacking TAZ showed increased levels of the Wnt-dependent transcriptional regulator β-catenin in both the cytoplasm and nucleus of kidney cells. TAZ interacted directly with the Dishevelled protein—a component of the Wnt signaling pathway—and depletion of TAZ or inhibition of Hippo signaling increased Wnt signaling in cultured cells. The Hippo pathway protein kinase LATS1 inhibits TAZ function by phosphorylation; interfering with this step diminished Wnt-dependent transcription. TAZ has also been implicated in signaling by transforming growth factor–β. Add to this the identification of TAZ as a component of a ubiquitin ligase complex that degrades an ion channel, and you have one busy protein indeed.

Dev. Cell18, 579 (2010).

Biophysics

Facilitated Folding

After a pollen grain is released from its anther, it must survive until it arrives at another flower's stigma. To preserve its precious cargo, the wall of the pollen grain folds in on itself to minimize water loss—a process named harmomegathy. The wall consists of a stiff, water-impermeable outer layer—the exine—and a pliant, water-permeable inner layer—the intine—which is exposed only at apertures in the exine. Katifori et al. show how the spatial structure of the pollen wall influences how the grain folds. On the basis of a model in which the bending deformation of the exine is interrupted at apertures and the Gaussian curvature remains constant, the authors numerically simulated pollen grain folding for the single-aperture Lilium longiflorum (lily) and the triple-aperture Euphorbia milii. These folding simulations closely matched those observed via scanning electron microscopy. Varying the aperture design revealed that effective closure to seal the grain required elongated apertures that reached almost to the poles or apertures that spanned the equator. At sufficiently small aperture size, the pollen grain undergoes mirror buckling, which is the lowest-energy solution for folding a closed sphere.